1. Field of the Invention
This invention relates generally to a spherical motor and, more particularly, to a spherical motor that includes a plurality of two-axis magnetic elements positioned on one of a field sphere or an armature sphere and a plurality of three-axis magnetic elements positioned on the other of the field sphere or the armature sphere, where the two-axis magnetic elements generate oscillating magnetic fields and the three-axis magnetic elements detect the oscillating magnetic fields and then provide an actuating magnetic torque to position the armature sphere.
2. Discussion of the Related Art
There is a need to accurately point various devices, such as antennas, sensors, detectors, etc., in a particular direction within a desired field of view. Currently, these devices are typically mounted on a two or three axis gimbal assembly where each axis includes a separate gimbal that is controlled by a separate motor to point the device in the desired direction. Such gimbal assemblies typically employ complex wrist and elbow joints that result in a relatively large and complex system sometimes unsuitable for certain applications.
Spherical motors are known in the art that require less space and can rotate and direct a device in three degrees of freedom. However, current spherical motor designs typically use extremely complex algorithms and modeling techniques that make their implementation difficult, impractical and cost prohibitive.
U.S. Pat. No. 5,410,232 issued to Smith illustrates this problem. The '232 patent discloses a spherical motor 10 including a spherical stator 12 surrounding a spherical rotor 18. Suitable bearings are provided so that the rotor 18 can rotate within the stator 12. A motor shaft 24 is mounted to the spherical rotor 18 and extends through a stator opening 26. The motor 10 provides three-axis positioning of the shaft 24 within the opening 26. The spherical rotor 18 includes a plurality of rotor magnets or poles 22 disposed on its outer surface, and the spherical stator 12 includes a plurality of stator poles 14 disposed on its inner surface. The stater poles 14 are controllable electric coils and the rotor poles 22 are permanent magnets defined by a magnetic core. The magnetic fields of the poles 14 and 22 interact to provide a torque on the rotor 18 to position the shaft 24.
The motor 10 includes an orientation sensing system 40 having a spherical grid pattern 42 provided on the outer surface of the rotor 18. The grid pattern 42 includes a set of symmetrically spaced radial lines continuously converging to a point P, where the motor shaft 24 is situated, and a set of parallel lines that are orthogonal to the radial lines. The system 40 uses a mathematical algorithm to determine the position of the rotor 18 relative to the grid pattern 42, and control the magnetic fields to position the shaft 24. Particularly, the system 40 uses the grid pattern 42 to determine the position of the rotor 18 and uses the magnetic field supplied to the rotor poles 22 to provide the desired torque.
The magnetic fields generated by the fixed magnet poles 22 are extremely complicated. Further, every time the rotor 18 moves, the magnetic field that the rotor 18 sees is different. Therefore, it is necessary to accurately know the position of the rotor 18 relative to the fixed poles 22. The sensing system 40 computes the magnetic field as seen by the rotor 18 each time the rotor 18 move. The rotor poles 22 are turned on and off to move the rotor 18 in the desirable direction. This operation requires a very elaborate position knowledge scheme for the rotor 18 employing complex algorithms. It would be desirable to provide a spherical motor that was much less complex to control.